In the BATF's eyes, I mean, not the caliber itself. The Glock pistol page mentions several variants in .380 which can't be imported. So what's the BATF's issue with .380 ACP?

__________________"The gun has played a critical role in history. An invention which has been praised and denounced... served hero and villain alike... and carries with it moral responsibility. To understand the gun is to better understand history."

“What is morality in any given time or place? It is what the majority then and there happen to like, and immorality is what they dislike.” - Alfred North Whitehead

It is to do with the Gun Control Act of 1968. The purpose of this was to restrict the importation of non "sporting" weapons into the US so they came up with a system whereby a pistol was awarded points based on a number of criteria and it needed a certain number of points to allow importation. With this system, less points were awarded for .380 rather than 9x19 and above as .380 ACP is deemed to have less of s "sporting purpose", so the .380 Glocks did not pass the test. Actually, the vast majority of Glocks would fail the test so they are actually imported with stuff like adjustable sights (more "sporting purpose" so more points than fixed sights) and have the sights swapped over in the US.